1. Field of the Invention
This invention relates generally to submersible, fluid powered pumps, and more particularly to a hydraulically operated fluid pump having a power piston reciprocated by pressurized hydraulic fluid, a pump housing having a power piston chamber in which the power piston is housed, a production piston chamber in which a production piston is housed, and an intermediate fluid and gas collection chamber disposed therebetween and the power piston, production piston, and a suction filter are connected by an elongate hollow tubular piston rod to reciprocate together.
2. Brief Description of the Prior Art
Mechanically operated positive displacement pumps, used for the extraction of petroleum fluids, brine, or water, are normally connected to surface machinery through an elongate operating puller, or sucker rod, which can operate only in straight and truly vertical bored holes. Surface operated mechanical pumps are not particularly suited for slanted wells, bent wells, and horizontal wells.
Due to the high cost of the surface machinery, such as the pumping jack and the sucker rod, and the maintenance costs of the mechanical system, the mechanically operated deep well pumps are cost effective only in the wells of high productivity. The output of mechanically operated pumps is limited to no more than one-sixth of the natural frequency of the elastic interaction of the sucker rod pipe and the bulk modulus of the pumped fluid.
Hydraulically operated single acting positive displacement piston pumps are a different type of pump wherein the power or pumping stroke and the return or recharge stroke is accomplished by the combination of hydraulic pressure and spring pressure, or the combination of hydraulic pressure and compressed gas pressure.
Most hydraulically operated pumps utilize a considerable volume of effective operating fluid and are limited to the number of pumping cycles per minute due to the cyclic operations of pressurization and recovery, the expansion and contraction of the pressure line, the fluid friction during downhole and return flow cycles, and fluid viscosity.
Roeder, U.S. Pat. No. 4,214,854 discloses a downhole hydraulically actuated pump having an engine reciprocatingly connected to a production pump. Power fluid is conducted downhole to the engine of the pump assembly, while production fluid and spent power fluid is conducted uphole to the surface. The pump assembly includes a housing within which spaced, axially aligned, cylindrical chambers reciprocatingly receive spaced engine and pump pistons which are connected together in a manner to enable the engine to reciprocate the production pump. A mechanically actuated valve assembly is contained within the engine piston and is arranged respective to various different flow passageways so that flow of power fluid through the engine forces the engine piston to reciprocate. The valve assembly includes a control rod and a valve element concentrically arranged respective to one another and to the engine piston. The valve element is reciprocated respective to the engine piston in response to reciprocation of the control rod. Abutment means formed on the engine cylinder shifts the control rod each stroke of the piston, thereby causing the valve element to shift respective to the piston, whereupon various different flow passageways are aligned with one another to cause power fluid to be effected upon the engine in such a manner that the engine piston reciprocates to thereby force the pump piston to be reciprocated within its cylinder.
Bennett, U.S. Pat. No. 4,295,801 discloses a small diameter fluid-driven pump for subterranean fluid sampling which has an elongated cylindrical body formed by a centrally disposed control valve block assembly and a pair of hollow motor piston chambers on opposite sides of the valve block and joined thereto. Within the centrally disposed control valve block assembly in axial alignment with the motor pistons are a spool pilot valve and a spool fluid distribution valve. The spool pilot valve is constructed to obviate stalling during its reciprocation under the impress of a power fluid directed thereto, and it functions to control the shifting of the distribution valve to which it is internally connected within the valve block assembly. The spool pilot valve includes a valve housing defining a large central piston chamber, a relatively small bore extending axially inwardly from one end of the valve housing, and into communication with the large central piston chamber, and a larger bore of smaller diameter than the central piston chamber extending axially into the opposite end of the valve housing into communication with the central piston chamber. A small piston is slidably positioned in the relatively small bore, a larger piston in the larger bore and a largest piston in the central piston chamber. A power fluid charging port communicates with the central piston chamber through the valve housing, and inlet and exhaust ports communicate with each of the bores. Sealing means on the largest piston in the central piston chamber allows power fluid to bleed from the power fluid charging port to opposite sides of the largest piston when this sealing means is directly aligned with the power fluid charging port.
Reese, U.S. Pat. No. 4,383,803 discloses a device for lifting liquid from boreholes comprising a pump which is located downhole in the region of a production formation and which consists of a fluid-actuated, double-action piston. The pump is connected by fluid pressure lines to a source of fluid pressure disposed above ground and a switching valve is connected to provide fluid pressure to alternate sides of the piston to effect reciprocation thereof.
Roeder, U.S. Pat. No. 4,544,335 discloses a downhole hydraulically actuated pump assembly of either the free or fixed type having a power piston which actuates a production plunger. A valve is concentrically arranged within the power piston. A stationary, hollow valve control rod extends through the power piston and through the valve, with a lower marginal end of the control rod terminating within the production plunger. Power fluid flows through the control rod and to the valve. As the power piston reciprocates within the engine cylinder, means on the control rod actuates the valve between two alternate positions so that power fluid is applied to the bottom face of the power piston to thereby cause the power piston to reciprocate upward; and thereafter, the control rod causes the valve to shift to the other position, whereupon spent power fluid is exhausted from the engine cylinder. The spent power fluid is admixed with production fluid and is conducted to the surface.
Strickland et al, U.S. Pat. No. 4,720,247 discloses an oil well reciprocating piston pump which is operated from a source at the earth's surface. The piston is hollow and also serves as a sealed cylinder for a free piston which is gas biased downwardly. The underside of the free piston is in contact with a body of oil displaceable from the sealed cylinder into the annular space between the hollow piston and its cylinder to bias the hollow piston toward the bottom end of its stroke.
Carrens, U.S. Pat. No. 4,925,374 discloses a sub-surface hydraulically operated engine for reciprocating an oilwell pumping unit which includes confined hydraulic fluid means for actuating a reversing valve and its lifter in order to change the upstroke motion to downstroke motion and vice-versa.
Roeder, U.S. Pat. No. 5,104,296 discloses a hydraulically actuated downhole pump powered by a fluid that is pumped downhole to an engine end thereof. The pump assembly has a pump end which is connected to a source of formation fluid so that the engine end drives the pump end and the pump end lifts produced fluid to the surface of the ground. The pump end has a pump barrel and a pump piston is reciprocatingly received in sealed relationship within the pump barrel. The engine end has an outer engine barrel, and an annular valve element is reciprocatingly received in sealed relationship within the outer barrel. The valve element moves up and down between two positions of operation while an engine piston reciprocates within the annular valve element and in so doing aligns various flow passageways in a manner to alternately apply power fluid to appropriate sides of the piston and valve element to force the engine piston to reciprocate. The valve element shifts between the two alternate positions at the end of each of the engine piston strokes. This configuration of an engine end reduces the complexity of the engine end and allows loose tolerances to be used in fabricating the engine end.
The present invention is distinguished over the prior art in general, and these patents in particular by a downhole hydraulically operated pump having a power piston reciprocated by alternating pressurized hydraulic fluid flow controlled at the surface by a hydraulic power control system which includes a spool valve and electric solenoid controlled directional valves which quickly reverse the flow direction. The pump housing, suspended in the well fluid of a cased well by a discharge tube, has a power piston chamber in which the power piston is housed, a production piston chamber in which a production piston is housed, and an intermediate fluid and gas collection chamber disposed therebetween. The power piston, production piston, and a suction filter are connected by an elongate hollow tubular piston rod to reciprocate together and the piston rod interior is in communication with the discharge tube. On up strokes, a series of check valves direct well fluid upwardly through the suction filter, the piston rod interior, through the production piston, into the production piston chamber, and from the production piston chamber through the production piston into the piston rod interior, and into the discharge tube. Entrapped well fluid in the production piston chamber is forced upwardly through a check valve, into the intermediate fluid and gas collection chamber, into the interior of the piston rod through a side bore, and to the surface through the discharge tube. On down strokes well fluid entrapped beneath the production piston is expelled upwardly through the production piston, into the piston rod interior, and into the discharge tube.